Difference determination between two sets of topologically congruent polygons

The goal of this project was the automation of control and evidence changes in a digital land register. The data in land registers needs to be frequently updated because some parcels of land could be sold or divided up between several inheritors, or simply because of a previous wrong input. Parcels are represented by a set of polygons. Changes are analysed inside a selected area. It can be small consisting of some ten parcels, or the whole city containing thousands of parcels. Newly measured parcels should be compared by an existing version in a land register. We have developed a new comparison algorithm, which successfully detects and analyses various changes. This program enables evidence of the changes besides updating the land register. In this way, a change can be tracked through a selected time period. The application is implemented in MS Visual C++ in Windows environment. The data are stored in Dbase3 files.